Generally speaking, high density printed circuit boards are constructed with several electrically conductive layers separated by dielectric layers. Some of the conductive layers are utilized to supply power and ground voltages. The remaining conductive layers are patterned for electrical signal interconnections among integrated circuit chips. Layer-to-layer interconnections are achieved by means of through-holes plated with electrically conductive material. In high density printed circuit boards, it has been normal practice to provide interconnections between adjacent conducting layers, which interconnections are commonly known as "vias".
Recently, there have been various suggestions of providing circuitized sub-composites which in turn are then assembled and laminated together to form the desired printed circuit board or card. For example, see U.S. Pat. Nos. 4,854,038; 4,864,722 and 4,868,350, all assigned to International Business Machines Corporation, the assignee of the present application, disclosures of which are incorporated herein by reference.
However, when employing laser technique to drill the interconnections, difficulties have been experienced in that it is necessary to provide a ring land having a relatively small etched center hole. In addition, in such arrangement, there is a tendency for the laser drilling to leave a residue of a thin layer of dielectrical material when drilling down to the buried layers of metal.